The Ministry of Defence's announcement that it is to award £3m in compensation to 360 veterans of chemical weapons tests has put the spotlight on the Science and Technology Laboratory at Porton Down, near Salisbury.

1899 Hague Declaration prohibits poison or poisoned arms. Russia and Britain signed, but the US did not. Russia later pulled out.

1914-1918 Chemical weapons, including chlorine, phosgene and mustard agents, are used during World War I, killing more than 90,000.

1916 Building work begins at Porton Down, near Salisbury, to create an experimental base for research into chemical warfare.

1920 Large-scale expansion of the site begins, initially focusing on the effects of mustard gas - experiments in which thousands of volunteers were to participate.

1938 UK government authorises development of offensive chemical warfare research and development as international relations deteriorate.

1940 After the outbreak of war, a secret group is set up at Porton Down to investigate biological warfare.

1945 Thousands of military personnel had taken part in trials at Porton Down during World War II, and as the war ended, volunteers began participating in nerve-agent trials there - a practice that was to continue until 1989.

1953 Leading Aircraftman Ronald Maddison participates in chemical experiments at Porton Down. Within an hour of being given sarin, he is dead. Military chiefs conduct an inquest in secret. Verdict: misadventure.

1956 UK begins running down its stocks of chemical warfare agents as the emphasis switches away from retaliation and back to defence.

1970s-1980s Scientists at Porton investigate the reported use of chemical weapons by Iraq against Iran and its own Kurdish population.

1989 US and Soviet Union reach agreement on destruction and non-production of chemical weapons.

Nerve-agent trials at Porton Down cease.

1995 Sarin used in an attack on the Tokyo underground.

1999 Wiltshire Police begin a four-year investigation into the human experiments at Porton Down following a complaint from veteran Gordon Bell, who was there nearly 50 years earlier.

2001 Government agrees to fund a health study for some Porton Down volunteers and announces a comprehensive survey of the Porton Down Volunteer Programme to investigate how volunteers were treated and what they were told. It promises to publish the findings.

2002 Ministry of Defence (MoD) helpline set up to enable Porton Down veterans to find out more about the trials they were involved in.

2003 Crown Prosecution Service decides to take no action following police investigation into the Porton Down trials.

2004 Fresh inquest into the 1953 death of Ronald Maddison returns a verdict of unlawful killing. The MoD launches a legal challenge.

2006 High Court rules in favour of Mr Maddison's family. As part of the settlement, the MoD admits "gross negligence".

17 January 2008 The BBC learns of a £3m out-of-court settlement between the MoD and veterans, under which the ex-servicemen will each receive £8,300 and an apology.

31 January 2008 The Ministry of Defence confirms it is to award £3m in compensation to 360 veterans of the tests without admission of liability. Defence minister Derek Twigg says the government "sincerely apologises to those who may have been affected".